Effects of regional analgesia versus intravenous morphine on electroencephalographic waves in response to noxious stimuli during general anesthesia

Abstract

Objectives We used the unprocessed electroencephalographic (EEG) analysis during general anesthesia (GA) to assess the effects of regional analgesia versus morphine (intravenously) on EEG waves in response to noxious stimuli (endotracheal intubation and skin incision). Background Noxious stimuli during GA cause EEG changes that represent the cerebral processing of noxious stimuli. Interpreting these changes could maintain balance between too much and too little anesthetics or using specific techniques (e.g. regional analgesia). Materials and methods Sixty consenting ASA I or II adult patients undergoing lower abdominal surgery were randomly assigned into two groups: the epidural group received 15 ml bupivacaine 0.25% epidurally to attain sensory analgesia up to T6 followed by induction of GA and the morphine group received intravenous morphine (0.1 mg/kg), 5 min before induction of GA. Arterial blood pressure, heart rate, respiratory rate, arterial O 2 saturation, and end-tidal CO 2 were monitored. EEG recordings were analyzed for the 10 Hz score, high-frequency variability index (HFVI), and delta power at different time points (1 min before and after the noxious stimuli). Results Within the same group, comparing the prenoxious with postnoxious stimuli, EEG changes showed highly significant statistical difference in both groups (e.g. in the epidural group, 10 Hz score changed by intubation from 0.27 ± 0.04 to 0.21 ± 0.03 and by incision from 0.31 ± 0.04 to 0.28 ± 0.03) - that is, marked decrease in its value. Comparing EEG parameters between both groups was insignificant. Comparing the preintubation and postintubation difference between both groups showed significant statistical difference regarding 10 Hz score (epidural = 0.06 ± 0.02 > morphine = 0.05 ± 0.01) and no significance regarding HFVI and delta power. Comparing the preincision and postincision difference between both groups showed significant statistical difference regarding 10 Hz score (epidural = 0.03 ± 0.01 Conclusion Using unprocessed EEG for monitoring the intraoperative adequacy of analgesia showed less response to noxious stimuli with epidural analgesia than systemic opioids as reflected by less EEG changes in the epidural group.